1. Field of the Invention
The present invention relates to a PWM IC, and more particularly, to a PWM IC, which is capable of adjusting the PWM signal according to the load of an electronic device coupled to the PWM IC.
2. Description of the Prior Art
A pulse width modulation (PWM) IC is typically utilized in a power supply system. The power supply system provides an output voltage according to a PWM signal generated by the PWM IC. The PWM signal is typically a square wave whose characteristics are defined by a high level, a low level, and a duty cycle. The duty cycle of the PWM signal determines the output voltage of the power supply system: when the duty cycle of the PWM signal increases, the power supply system accordingly outputs a greater output voltage, however, when the duty cycle of the PWM signal decreases, the power supply system accordingly outputs a lower output voltage. Therefore, a power supply system typically utilizes a PWM IC to determine the output voltage.
When a power supply system is utilized to power electronic devices such as a motherboard, a graphic card, a notebook, or a cell phone, the output voltage of the power supply system must change in accordance with the load of the electronic device. For example, when the load of the electronic device increases, the output voltage of the power supply system must increase to ensure that the electronic device can be operated in a proper condition. Alternatively, when the load of the electronic device decreases, the output voltage of the power supply system must decrease correspondingly to reduce the system power consumption or protect the electronic device from damage by an abnormal voltage.
Since the output voltage of the power supply system is dominated by the PWM signal of the PWM IC, the output voltage can be adjusted by changing the PWM signal. Typically, adjusting the PWM signal is implemented by utilizing an outer control signal such as a GPIO signal to adjust the reference voltage of the PWM IC or utilizing an outer circuit to change the digital ID input signal of the PWM IC to change the duty cycle or the output voltage. However, these two methods do not adjust the output voltage real-time directly corresponding to the load of the electronic device. Moreover, the outer circuit along with an outer program, which controls the outer circuit, results in a higher cost and inconvenience.